1. Field of the Invention
Present invention relates to non-inflammable light-weighing tough boards, in particular, corrugated cardboards to be used for structural and decorative material in housings and buildings, such as, ceiling decorative boards, sliding door overlays, partitions and so on.
2. Description of the Prior Art
While there are used for manufacturing non-inflammable interior construction materials such as ceiling boards etc., non-inflammable excelsior boards and boards made from mineral wools, such as, gypsum whisker, whiskered blast furnace slag, glass wool and so on, all these prior art materials are heavy in weight and are inconvenient in the transport and in the assemblage work etc. On the other hand, there have also been found in the market sheet products made or paper toughend by impregnating with synthetic resins, such as phenol resin etc. However, they are not cost-saving, since high price chemical products are used for the manufacture thereof.